Stator for a rotating electrical machine

ABSTRACT

A stator for a rotating electrical machine comprises a stator mass comprising teeth and notches between the teeth, each of the notches being, on the air gap side, completely closed, electrical conductors being housed in the notches, the electrical conductors forming a fractional winding, for which the ratio q defined by q=Ne/(2 pm) is written as an irreducible fraction z/n, z and n being two non-zero integers, n being different from 1, wherein Ne is the number of stator notches, m the number of winding phases and p the number of pairs of stator poles.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage under 35 USC § 371 ofInternational Application No. PCT/FR2020/050382, filed 27 Feb. 2020which claims the priority of French application 1902069 filed on Feb.28, 2019, the content of which (text, drawings and claims) isincorporated here by reference.

BACKGROUND

The present invention relates to rotating electrical machines, and moreparticularly to the stators of such machines.

The invention relates more particularly to synchronous or asynchronousAC machines. It relates in particular to traction or propulsion machinesfor electric motor vehicles (Battery Electric Vehicle) and/or hybridmotor vehicles (Hybrid Electric Vehicle—Plug-in Hybrid ElectricVehicle), such as individual cars, vans, trucks or buses. The inventionalso applies to rotating electrical machines for industrial and/orenergy production applications, in particular naval or wind powerapplications.

PRIOR ART

Electrical machines used in automotive applications most often have anumber of notches per pole and per whole phase, and open or semi-openstator notches.

In US 2003/0214196, US 2007/0018525, and U.S. Pat. No. 7,348,705, thenotches are semi-open and house U-shaped electrical conductors, theelectrical conductors being distributed between two sets of independentcoils on four layers, two layers per set of coils. The conductors of twodifferent sets of coils are not electrically connected together in thestator. The connections between the phases are made outside the stator,in a terminal box. In US 2007/0018525, the stator has a number ofnotches per pole and per fractional phase.

In CN205583868, the stator has a number of notches per pole and perfractional phase, with notches which are entirely closed on the side ofthe air gap, and closed on the side opposite the air gap by an attachedyoke. However, the stator has a concentrated winding, being wound on atooth.

In patent application US 2014/0319953, the notches of the stator are notclosed.

Moreover, in known stators, the stator yoke has fully open or semi-opennotches in the direction of the air gap, so as to allow the introductionof the conductors of the windings. Generally, the semi-open notchesreceive electrical conductors of circular cross-section arranged inbulk, while the fully open notches house electrical conductors ofrectangular cross-section, arranged in a row.

Stators are also known in which the notches are closed by non-magneticor semi-magnetic shims. However, such shims may come off and interferewith the operation of the machine.

US 2010/0001609 relates to a stator in which the notches are closed, andreceive U-shaped electrical conductors of rectangular cross-section,which are each connected to a conductor of the adjacent notch, in orderto form a series wave winding. The winding is not fractional.

Patent application FR 3,019,947 describes a stator comprising a toothedring comprising teeth interconnected by material bridges and definingnotches therebetween for receiving coils, the notches being openradially outwardly. The notch openings are closed by a yoke attached tothe toothed ring.

There is a need to benefit from a stator for a rotating electricalmachine that is easy to assemble allowing efficient filling of thenotches, while ensuring satisfactory electromagnetic performance. Thereis also a need to further improve the stators of electrical machines,and in particular to reduce torque ripples, electromagnetic vibrationsand noise.

SUMMARY

Stator

The noted need is met and achieved, owing to the disclosed stator for arotating electrical machine according to one of its aspects, the statorcomprising a stator mass comprising teeth and notches between the teeth,each of the notches being, on the air gap side, at least partiallyclosed, in particular completely closed, electrical conductors beinghoused in the notches, the electrical conductors forming a winding, inparticular a single fractional winding, for which the ratio q defined byq=Ne/(2 pm) is written as an irreducible fraction z/n, z and n being twonon-zero integers, n being different from 1, where Ne is the number ofstator notches, m is the number of winding phases and p is the number ofpairs of stator poles. At least some of the electrical conductors, ifnot a majority of the electrical conductors, can be in the form of pins,in particular U or I pins.

The noted need is met and achieved, independently of or in combinationwith the above, by the provision of a stator for a rotating electricalmachine, comprising a stator mass comprising teeth and notches betweenthe teeth, each of the notches being, on the air gap side, completelyclosed, electrical conductors being housed in the notches, theelectrical conductors forming a fractional winding, for which the ratioq defined by q=Ne/(2 pm) is written as an irreducible fraction z/n, zand n being two non-zero integers, n being different from 1, where Ne isthe number of stator notches, m is the number of winding phases and p isthe number of pairs of stator poles. The stator may have one or more ofthe features mentioned above or below. In particular, at least some ofthe electrical conductors, if not a majority of the electricalconductors, can be in the form of pins, in particular U or I pins, andextend axially into the notches.

In another aspect, independently of or in combination with the above,the stator for a rotating electrical machine comprises a stator masscomprising teeth and notches between the teeth, each of the notchesbeing, on the air gap side, at least partially closed, electricalconductors being housed in the notches and being distributed in at leasttwo layers, in particular in only two layers, the electrical conductorsforming a single fractional winding, for which the ratio q defined byq=Ne/(2 pm) is written as an irreducible fraction z/n, z and n being twonon-zero integers, n being different from 1, where Ne is the number ofstator notches, m is the number of winding phases and p is the number ofpairs of stator poles. The stator may have one or more of the featuresmentioned above or below. In particular, at least some of the electricalconductors, if not a majority of the electrical conductors, can be inthe form of pins, in particular U or I pins, and extend axially into thenotches.

Fractional Winding

A winding is made up of a number of phases m offset in space in such away that when supplied by a multi-phase current system, they produce arotating field.

The electrical conductors can form a single winding. “Single winding”means that the electrical conductors are electrically connected togetherin the stator, and that the connections between the phases are made inthe stator, and not outside the stator, for example in a terminal box.

The electrical conductors can form a distributed winding. The winding isnot concentrated or wound on a tooth.

The winding is fractional in the disclosed stator. The winding can befractional.

For a fractional winding, the number of notches per pole and per phaseis fractional, i.e. the ratio q defined by q=Ne/(2 pm) is written as anirreducible fraction z/n, z and n being two non-zero integers, n beingdifferent from 1, where Ne is the number of notches of the stator, m thenumber of phases of the winding and p the number of pairs of statorpoles.

In one embodiment, q may be strictly greater than 1.5, in particulardifferent from 1.5, better still greater than or equal to 2.25, forexample notably equal to 5/2 or 7/2. It is thus possible to reduce thetorque harmonics.

The number of notches in the stator can be between 18 and 96, betterstill between 30 and 84, being for example 18, 24, 27, 30, 36, 42, 45,48, 54, 60, 63, 72, 81, 92, 96, or even more preferably being 60 or 63.The number of poles of the stator can be between 2 and 24, or evenbetween 4 and 12, for example 6 or 8.

The combination of the number of notches/the number of stator poles canbe chosen from the combinations of the following list, which is notexhaustive: 30/4, 42/4, 45/6, 63/6, 60/8, 84/8.

In one embodiment, the combination of the number of notches/the numberof stator poles is 60/8. In this case we have q=60/(2*4*3)=5/2.

In one embodiment, the combination of the number of notches/the numberof pairs of stator poles is 63/6. In this case we have q=63/(2*3*3)=7/2.

More broadly, the combination between the number of notches Ne and thenumber of pairs of stator poles p may be one of those checked in table 1below, for a three-phase winding.

A higher number of notches per pole and per phase allows betterfiltering of harmonics.

TABLE 1 Combinations of the number of notches Ne and the number of pairsof stator poles p

1

2

3

4

5

6

7

8

9

10

11

indicates data missing or illegible when filed

The number of phases is three in this case, but the number of phases canbe different, two for example, the machine then comprising a two-phasewinding, or for example 5, 6 or 9. Preferably, the winding is polyphase.

We will now explain the advantages of a fractional winding, possiblyassociated with closed notches.

The torque ripples and the magnetic forces which depend on the spectrumof the induction in the air gap are the main sources of noise ofelectromagnetic origin. This noise is manifested on the one hand by thetorque ripples which interact with the transmission system and on theother hand by the magnetic forces which apply to the stator of themachine, which can, depending on their amplitudes and their frequencies,excite the eigen modes of the machine and thus make it enter intoresonance.

The magnetic force and torque ripple harmonics which are at the sourceof these phenomena are due to the spatial harmonics of notches. Theseharmonics come from the variation of the air gap permeance, whichdepends on the notch opening and the discrete distribution of themagnetomotive force.

In the case of open or semi-open notch machines, the permeance spectrumis rich in harmonics, which increases the harmonic rate of the magneticforces; the stator yoke can then be more subject to resonance problems,since its rigidity is lower if the notch opening is larger.

In whole-pitch machines, in order to reduce the harmonics of the air gapfield, a relatively high number of notches per pole and per phase isoften adopted, for example greater than 3, as well as a shortening ofthe opening pitch of the coils. In order to reduce the notch harmonics,which are due to the distribution of the winding, it is possible totwist the stator or the rotor of the machine. However, this method addsan additional manufacturing step.

It is understood that the fractional winding makes it possible to reducethe harmonic content of the magnetomotive force in the air gap, thusreducing the torque ripples and the amplitudes of the radial andtangential magnetic pressures.

For example, a comparison of the harmonic rates between a 48 notch, 8pole machine with a number of notches per pole and per whole phase withand without shortening and a 60 notch, 8 pole machine with a number ofnotches per pole and per fractional phase is illustrated in Table 2below, which shows the advantage of the fractional pitch.

TABLE 2 Harmonic ratio in p.u between a whole and fractional number qMachine Harmonic rate (p.u) q whole without shortening 1 q whole withshortening 0.76 q fractional 0.15

Table 3 below shows a comparison of the torque ripples in % between 48slot, 8 pole machines with a number of notches per pole and per wholephase with a straight rotor and a twisted rotor and 72 notch, 6 polemachines with a number of notches per pole and per whole phase with astraight rotor and a twisted rotor on the one hand, and on the otherhand a 63 notch, 6 pole machine with a number of notches per pole andper fractional phase with a straight rotor. The relevance of afractional winding is understood in reducing the torque ripple ratewithout having to twist the rotor.

TABLE 3 Torque ripple in [%] Torque ripple [%] Machine 4000 rpm 11000rpm Full winding 48/8 + straight rotor 19.2 22.1 Full winding 48/8 +twisted rotor 5.5 9.1 Full winding 72/6 + straight rotor 14.6 15.3 Fullwinding 72/6 + twisted rotor 2.4 5.2 63/6 fractional winding + straightrotor 2.3 4.6

The electrical conductors can be placed in series in a so-called wavewinding or in a so-called overlapping winding.

The term “wave winding” is understood to mean a winding in which theelectrical conductors of the same phase and of the same pole areelectrically connected to one another so that, for a winding path, theelectric current of the phase circulates in the electrical conductorsrotating about the axis of rotation of the machine, always in onedirection. For a winding path, the electrical conductors of the samephase and the same pole do not overlap when observed perpendicular tothe rotation axis of the machine.

The term “overlapping winding” is understood to mean a winding in whichthe electrical conductors of the same phase and of the same pole areelectrically connected to one another so that the electric current ofthe phase circulates in the electrical conductors rotating about theaxis of rotation of the machine alternatingly in one direction, then inthe other. For a winding path, the electrical conductors of the samephase and the same pole overlap when observed perpendicular to therotation axis of the machine.

The winding may comprise a single winding path or several winding paths.The current of the same phase flows by winding path in an “electricalconductor.” “Winding path” means all the electrical conductors of themachine which are traversed by the same electric current of the samephase. These electrical conductors can be connected to each other inseries or in parallel or in series-parallel. In the case where there isonly one channel, the electrical conductors are connected in series. Inthe case where there are several channels, the electrical conductors ofeach channel are connected in series, and the channels are connected inparallel.

Electrical Conductors

The current of the same phase of a winding path flows in an “electricalconductor.”

In each notch there can be one or more layers. “Layer” refers to theseries conductors belonging to the same phase arranged in the samenotch. In each layer of a notch, there are the electrical conductors ofthe same phase. In general, the electrical conductors of a stator can bedistributed in one layer or in several layers, for example two, three orfour layers. When the electrical conductors are distributed in a singlelayer, each notch only houses electrical conductors of the same phase.

In the disclosed stator, the electrical conductors can be divided intoat least two layers, in particular into only two layers. In this case,one or more notches can house electrical conductors of two differentphases. This is always the case for a winding with shortened pitch.

In one embodiment, the winding may not comprise more than two layers. Inone embodiment, it is notably devoid of four layers.

At least a first electrical conductor housed in a first notch can beelectrically connected to a second electrical conductor housed in asecond notch, at the outlet from said notches.

“Electrically connected” means any type of electrical connection, inparticular by welding, with different possible welding methods, inparticular laser, induction, friction, ultrasound, vibrations orbrazing, or by mechanical clamping, in particular by crimping, screwingor riveting for example.

The first and second notches are preferably non-consecutive.

The first and second electrical conductors can be electrically connectedto the outlet of the first and second notches, that is to say that theelectrical connection is formed on the electrical conductors just aftertheir exit from the two notches, at an axial end of the stator mass. Theelectrical connection can be made in a plane perpendicular to the axisof rotation of the machine. The plane of the electrical connection canbe less than 60 mm away from the stator mass, better still less than 40mm away, for example 27 mm or 38 mm approximately.

A majority of the electrical conductors housed in a first notch can eachbe electrically connected to a respective second electrical conductorhoused in a second notch, at the outlet of said notches. At least onenotch, better still a majority of the notches, or even more than half ofthe notches, better still more than two-thirds of the notches, or evenall of the notches, may comprise first electrical conductors eachelectrically connected to a respective second electrical conductorhoused in a second notch, at the outlet of said notches.

In one embodiment, all the electrical conductors having a free endlocated at the same circumferential position about the axis of rotationof the machine, regardless of their radial position, are electricallyconnected together.

The first and second electrical conductors can each comprise an obliqueportion. The oblique portions may extend in a circumferential directionabout the axis of rotation of the machine. The two oblique portions canbe configured to converge toward one another and thus allow theelectrical connection to be made.

An electrical conductor can comprise two oblique portions, one at eachof its two ends. The two oblique portions of the same electricalconductor can extend in opposite directions. They can be symmetricalwith respect to each other.

A majority of the electrical conductors can comprise one or more obliqueportions as described above.

The electrical conductors can be arranged in the notches in adistributed manner. “Distributed” means that the outgoing and returnelectrical conductors are each housed in different and non-consecutivenotches. At least one of the electrical conductors can pass successivelythrough two non-consecutive notches.

The electrical conductors can be arranged in a row in the notches. “Row”means that the electrical conductors are not arranged in the notches inbulk, but in an orderly manner. They are stacked in the notches in anon-random manner, for example arranged in one or several rows ofaligned electrical conductors, in particular in the radial and/orcircumferential direction.

The electrical conductors may have a generally rectangularcross-section, in particular with rounded edges. The circumferentialdimension of an electrical conductor can correspond substantially to thewidth of a notch. Thus, a notch may comprise only a single electricalconductor in its width. The width of the notch is measured in itscircumferential dimension about the axis of rotation of the machine.

Electrical conductors can be adjacent to each other by their long sides,otherwise called the flat.

Optimizing the stack can make it possible to place a greater quantity ofelectrical conductors in the notches, and therefore to obtain a statorof greater power at a constant volume.

Each notch can comprise from 2 to 36 electrical conductors, inparticular from 2 to 24, better still from 2 to 12 electricalconductors. Each notch may comprise from two to eight electricalconductors, in particular from two to four electrical conductors, forexample two or four electrical conductors. In alternative embodiment,each notch comprises two electrical conductors. In another alternativeembodiment, each notch comprises four electrical conductors.

Pins

At least some electrical conductors, if not a majority of the electricalconductors, can be in the form of U or I pins. The pin can be U-shaped(a “U-pin”) or straight, being I-shaped (an “I-pin”).

The pin and flat electrical conductors increase the filling coefficientof the notch, making the machine more compact. Owing to a high fillingcoefficient, the thermal exchanges between the electrical conductors andthe stator mass are improved, which makes it possible to reduce thetemperature of the electrical conductors inside the notches.

Furthermore, the manufacture of the stator can be facilitated by theelectrical conductors in pin form. In addition, the winding with pinscan be modified easily by changing only the connections between the pinsat the coil heads. Finally, since the pins do not need to have opennotches, it is possible to have closed notches which make it possible tohold the pins, and it is therefore possible to eliminate the step ofinserting stator shims.

There is no need in this case for an attached yoke, which makes itpossible to improve the mechanical strength of the stator and itsthermal conductivity.

As an alternative, the electrical conductors could comprise round wire.In one embodiment, the stator may comprise a magnetic hoop as definedbelow and electrical conductors in the form of a round wire. These canbe inserted into the notches on the air gap side before the hoop isfitted.

Some of the electrical conductors, or even a majority of electricalconductors, extend axially in the notches. The electrical conductors canbe introduced into the corresponding notches by one or both axial endsof the machine.

An I-shaped electrical conductor has two axial ends each placed at oneof the axial ends of the stator. It passes through a single notch, andcan be welded at each of its axial ends to two other electricalconductors, at the axial ends of the stator.

A U-shaped electrical conductor has two axial ends both placed at one ofthe axial ends of the stator. It passes through two different notches,and can be welded at each of its axial ends to two other electricalconductors, at the same axial side of the stator. The bottom of the U isplaced on the other axial side of the stator.

An electrical conductor, being in the shape of a U-pin, may comprise afirst and a second leg extending axially respectively in first A andsecond R notches. Reference may also be made to the opening of theelectrical conductor. The first A and second R notches are separated bya number Nd of teeth. This is the number of teeth between the outgoingnotch and the return notch of the same electrical conductor. The numberNd of teeth can be strictly greater than 5, being for example greaterthan or equal to 6. It may for example be 6, 7 and/or 8, or 9, 10 and/or11.

The number Nd of teeth may be the same for all the electrical conductorsof the stator in the form of U-shaped pins. For the number Nd of teeth,reference may also be made to the pitch of an electrical conductor. Whenthe latter is the same for all the electrical conductors of the statorwhich are in the form of a U-shaped pin, it is thus possible tofacilitate the manufacture of the U-shaped pins, and the step ofpositioning them in the stator mass is simplified, in particular theirinsertion. Advantageously, such a configuration makes it possible toimprove the smoothing of the field in the air gap, and to reduce theharmonics of the stator.

Strands

In one embodiment, each electrical conductor may comprise one or morestrands (also called “wire”). “Strand” refers to the most basic unit forelectrical conduction. A strand can be of round cross-section, which maythen be called “wire,” or may be flat. The flat strands can be shapedinto pins, for example U or I pins. Each strand is coated with aninsulating enamel.

The fact that each notch can comprise several conductors and/or severalstrands makes it possible to minimize losses by induced currents, orJoule AC losses, which vary with the square of the supply frequency,which is particularly advantageous when the operating speed is high. Itis thus possible to obtain better efficiency at high speed.

The presence of closed notches can make it possible to obtain areduction in the leakage fluxes seen by the conductors, which leads to areduction in eddy current losses in the strands.

In one embodiment, each electrical conductor may comprise one or severalpins, each forming a strand, as explained above. In this case, all thestrands of the same electrical conductor can be electrically connectedto each other at the outlet of the notch. The strands electricallyconnected to each other are placed in short circuit. The number ofstrands electrically connected together may be greater than or equal to2, being for example between 2 and 12, being for example 3, 4, 6 or 8strands.

Several strands can form the same electrical conductor. The sameelectric current of the same phase circulates in all the strands of thesame electrical conductor. All the strands of the same electricalconductor can be electrically connected to each other, in particular atthe outlet of the notch. All the strands of the same electricalconductor can be electrically connected to each other at each of theirtwo axial ends, in particular at the outlet of the notch. They can beelectrically connected in parallel.

All the strands of all the electrical conductors having a free endlocated at the same circumferential position about the axis of rotationof the machine, regardless of their radial position, can be electricallyconnected to one another.

In one embodiment, each electrical conductor comprises a single strand.In another embodiment, each electrical conductor comprises threestrands.

In the case where a notch comprises two electrical conductors, a notchcan therefore house two strands, or in a variant six strands, forexample, distributed between the two electrical conductors.

In an alternative, a notch comprises four electrical conductors. Eachelectrical conductor can comprise two strands. The notch then houseseight strands, distributed between the four electrical conductors.

The strands can be positioned in the notch so that their circumferentialdimension around the axis of rotation of the machine is greater thantheir radial dimension. Such a configuration allows a reduction in eddycurrent losses in the strands.

A strand may have a width of between 1 and 5 mm, for example of theorder of 2.5 or 3 mm. The width of a strand is defined as its dimensionin the circumferential direction about the axis of rotation of themachine.

A strand may have a height of between 1 and 4 mm, for example of theorder of 1.6 or 1.8 mm. The height of a strand is defined as itsthickness in the radial dimension.

A ratio of the width of a strand to its height can be between 1 and 2.5,better still between 1.2 and 2, or even more preferably between 1.4 and1.8, being for example 1.56 or 1.66.

In another embodiment, a strand may have a height of between 2 and 8 mm,for example of the order of 4.75 mm. The height of a strand is definedas its thickness in the radial dimension. A ratio of the width of astrand to its height can be less than 1, for example between 0.9 and0.2, or even between 0.8 and 0.3, being for example about 0.5 to 0.6.

The electrical conductors can be made of copper or aluminum.

Insulators

The electrical conductors are electrically insulated from the outside byan insulating coating, in particular an enamel. The electricalconductors can be separated from the walls of the notch by an insulator,in particular by at least one insulating sheet. Such a sheet insulatorallows better insulation of the electrical conductors with respect tothe stator mass. The use of closed notches can make it possible toimprove the retention of the insulators around the electrical conductorsin the notches.

Partially Closed or Fully Closed Notches

The notches can be at least partially closed. A partially closed notchmakes it possible to provide an opening at the air gap, which can beused, for example, to install the electrical conductors for filling thenotch. A partially closed notch is in particular formed between twoteeth which each comprise pole shoes at their free end, which close thenotch at least in part.

In an alternative, the notches can be completely closed. The term “fullyclosed notch” denotes notches which are not open radially toward the airgap.

The notches can be closed on the air gap side by a magnetic hoop. Thehoop can be attached to the teeth on the side of the air gap. Themagnetic hoop can preferably have the same magnetic permeability as thestator. It can in particular be made of the same material as the statormass. It can be generally annular in shape and placed in the air gap. Itforms bridges of material between the teeth, which close the notches onthe side of the air gap. These material bridges are not in one piecewith the teeth defining the notch. This magnetic hoop can in particularbe in a single piece over the entire circumference of the stator. It canbe formed from a stack of rolled sheets.

The magnetic hoop may have at least one localized constriction formed byat least one groove. The hoop may in particular comprise at least onegroove per material bridge closing a notch, said grooves possibly beingarranged in front of each of the notches.

When using a hoop, it is then possible to use round wire electricalconductors.

In a variant, the stator does not include an added hoop serving to closethe notches.

In one embodiment, at least one notch, or even each notch, can becontinuously closed on the side of the air gap by a material bridgeformed in one piece with the teeth defining the notch. All the notchescan be closed on the side of the air gap by material bridges closing thenotches. The material bridges may have come in one piece with the teethdefining the notch. The stator mass is then devoid of any cutout betweenthe teeth and the material bridges closing the notches, and the notchesare then continuously closed on the side of the air gap by the materialbridges coming in one piece with the teeth defining the notch.

In addition, the notches can also be closed on the side opposite the airgap by an attached yoke or in one piece with the teeth. The notches arethen not radially outwardly open. The stator mass may have no cutoutbetween the teeth and the yoke.

In one embodiment, each of the notches has a continuously closedcontour. “Continuously closed” means that the notches have a continuousclosed contour when viewed in cross-section, taken perpendicular to theaxis of rotation of the machine. It is possible to go all the way aroundthe notch without encountering a cutout in the stator mass.

The presence of the closed notches makes it possible to improve theperformance of the electrical machine in terms of the quality of themagnetic field in the air gap, by minimizing the harmonic content andthe eddy current losses in the electrical conductors, and the leakagefluxes in the notches, as well as the fluctuations of the magnetic fieldin the air gap and heating of the machine. The closed notches make itpossible to have a closed cylindrical air gap, to reduce the leakagefluxes in the notches, which makes it possible to reduce the AC lossesin the stator winding. The battery life is therefore extended owing tothe increased efficiency of the machine due to the reduction in AClosses.

In addition, the presence of these closed notches makes it possible toimprove the mechanical rigidity of the stator, by mechanicallystrengthening the stator and by reducing vibrations. In particular, itis possible to obtain a separation of the resonance frequencies from thedeformation mode corresponding to 2p, p being the number of pairs ofstator poles. Reducing the vibrations can help make the operation of themachine quieter, which can be particularly advantageous when the statoris intended to be associated with a gearbox system.

Also, closing the notch can reduce the stray capacitance between thestator windings and the rotor, which reduces leakage currents and canavoid having to use drain rings or brushes for the shaft currents.

The stator mass can be produced by stacking magnetic sheets, the notchesbeing formed by cutting the sheets. The stator mass can also be producedby cutting from a mass of sintered or agglomerated magnetic powder. Theclosing of the notches on the side of the air gap is obtained bymaterial bridges in one piece with the rest of the sheets or of theblock forming the stator mass.

The stator does not have any attached magnetic shims for closing thenotches. This eliminates the risk of accidental detachment of theseshims.

Material Bridges

The stator mass may comprise teeth formed between the notches, which areinterconnected on the side of the air gap by material bridges. Thus,each notch is closed on the side of the air gap by a material bridgeinterconnecting two consecutive teeth of the stator mass. The materialbridges each connect two teeth adjacent to their base on the side of theair gap and define the bottom of the notch between these teeth on theside of the air gap.

The material bridges are in one piece with the adjacent teeth.

The two consecutive teeth are connected on the opposite side by a yoke.The yoke can be made in one piece with the teeth. The stator can thus bewithout a yoke attached to a serrated ring.

As mentioned above, the absence of opening of the notches toward the airgap makes it possible to avoid producing electromagnetic disturbances,in particular an increase in the “magnetic” air gap due to the fluxfringes, higher iron losses at the rotor surface for the same reason, oralternatively pulsating torques, as well as radial forces and Joule AClosses. The electromagnetic performance of the machine is improved.

The material bridges can be made so as to be magnetically saturatedduring machine operation. This limits the passage of the flux from onenotch to another without preventing the passage of the flux from therotor to the stator.

The material bridges are preferably not deformable. This increases thestiffness of the stator and improves the life of the electrical machine.

The smallest width of the material bridges is for example between 0.2and 0.5 mm. It can be of the order of 0.35 mm, for example.

The width of the material bridge can be of the same order of magnitudeas the thickness of the sheet.

For example, the stator mass is in the form of stacked sheet metal,having teeth interconnected at their base on the side of the air gap bymaterial bridges.

The material bridges are in one piece with the teeth.

Grooves

The material bridges can each have at least one localized constrictionformed by at least one groove. To obtain saturation, the cross-sectionof the material bridge which is available for the passage of the fluxcan be locally reduced, for example by providing a groove.

Preferably, the grooves are open toward the notches.

The bottom of the notches on the side of the material bridge has atleast one bearing surface, better still at least two bearing surfaces,oriented transversely, and the bottom of the groove is set back relativeto the bearing surface(s). The bearing surface(s) may be orientedobliquely with respect to the radial axis of the corresponding notch ororiented perpendicular to this axis. The groove forms a break in slopewith respect to the bearing surface(s). The electrical conductors,preferably of substantially rectangular cross-section, inserted into thecorresponding notch preferably bear against the bearing surfaces and areset back relative to the bottom of the groove. Preferably, theelectrical conductors are not in contact with the groove. The bearingsurface(s) are preferably flat. The bottom of the notch can be flat,except for the groove. This allows good filling of the notches by theelectrical conductors in the case of electrical conductors ofrectangular cross-section, allowing the coils to rest flat in the bottomof the notches.

The groove in the bottom of the notch preferably forms a clearancebetween the material bridge and the corresponding electrical conductor.

The material bridge may comprise at least two grooves as describedabove, for example two grooves per notch.

The groove(s) can be centered with respect to the notch(es), or on thecontrary be offset with respect to a plane of symmetry of the notch(es).

Preferably, the groove(s) each have a curved profile in cross-section ina plane perpendicular to the axis of the stator, in particular ofsubstantially semi-circular cross-section. The bottom of the groove maybe in the form of a circular arc, or of any other suitable shape, forexample semi-elliptical or wavy.

The inner surface of the stator is preferably cylindrical.

Notches

At least one notch, more preferably all the notches, may be generallyrectangular in cross-section.

At least one notch, better still all the notches, may comprise radialedges having a rib, in particular each having a rib. The rib can make itpossible to improve the retention of the electrical conductors in thenotches. In addition, the rib can help minimize AC Joule losses.

The rib may extend parallel to the axis of rotation of the machine.

The rib can be placed in a central part of the radial edges, for examplehalfway between the bottom of the notch and the material bridge closingit. In a variant, at least one notch, better still all the notches, cancomprise radial edges each having several ribs, for example two orthree. This can in particular be useful in the case where the notch isintended to receive three, four, six or eight electrical conductors. Thenotch may comprise a rib between each of the layers of electricalconductors.

In an alternative embodiment, the radial edges are rectilinear, beingdevoid of ribs.

At least one notch can have opposite radial edges parallel to eachother, better still all the notches have radial edges parallel to eachother. The width of a notch is preferably substantially constant overits entire height. There is thus a better filling rate of the notches.

In an alternative, the radial edges of the notches are not parallel toeach other.

At least one notch, better still all the notches, can have a rectilinearbottom, in the form of an arc of a circle or the like. The bottom of thenotch is the bottom of the notch located on the side of the yoke,opposite the material bridge and the air gap.

At least one notch, better still all the notches, can have a ratio ofthe length of the notch to its width of between 2 and 6, better stillbetween 3 and 4. The width of a notch corresponds to its dimension inthe circumferential direction measured about the axis of rotation of themachine, and its length to its dimension in the radial direction.

The stator may comprise a sensor for measuring the temperature of theelectrical conductors, the sensor being arranged in the notch, forexample a thermocouple. This sensor can be housed at least partly in thegroove of the material bridge closing the notch. The sensor is forexample housed in a space between the conductor closest to the materialbridge and the material bridge.

The notches can be configured to allow the passage of a coolant. Some orall of the notches can accommodate ducts for circulating a coolant, orthe coolant can flow directly through the notches. The coolant can flowin the bottom of the notch, and/or toward the material bridge, and/orbetween the electrical conductors, for example between two layers ofelectrical conductors. The coolant can be a gas, for example air, or aliquid, for example water or oil.

At least one tooth, better still all the teeth, may be generallytrapezoidal in cross-section. At least one tooth, better still all theteeth, may have divergent edges moving away from the axis of rotation ofthe machine.

The stator mass can be produced by stacking sheets. The teeth areconnected to each other by material bridges, and on the opposite side bya yoke. The closed notches can be produced entirely by cutting from thesheets. Each sheet of the stack of sheets can be in one piece.

Each sheet is for example cut from a magnetic steel sheet or a sheetcontaining magnetic steel, for example steel 0.1 to 1.5 mm thick. Thesheets can be coated with an electrically insulating varnish on theiropposite faces before they are assembled within the stack. Electricalinsulation can also be obtained by heat treatment of the sheets, ifnecessary.

In an alternative, the stator mass can be made from a compacted oragglomerated magnetic powder.

Machine and Rotor

Also disclosed is a rotating electrical machine, such as a synchronousmotor or a synchronous generator, comprising a stator as defined above.The machine can be synchronous or asynchronous. The machine can be areluctance machine. It can constitute a synchronous motor.

The maximum speed of rotation of the machine can be high, being forexample greater than 10,000 rpm, better still greater than 12,000 rpm,being for example of the order of 14,000 rpm to 15,000 rpm, or even20,000 rpm or 25,000 rpm. The maximum speed of rotation of the machinemay be less than 100,000 rpm, or even 60,000 rpm, or even less than40,000 rpm, better still less than 30,000 rpm.

The rotating electrical machine may comprise a rotor. The rotor can be apermanent magnet rotor, with surface or buried magnets. The rotor can bein flux concentration. It can comprise one or more layers of magnetsarranged in an I, a U, or a V. Alternatively, it may be a wound orsquirrel cage rotor, or a variable reluctance rotor.

The diameter of the rotor may be less than 400 mm, better still lessthan 300 mm, and greater than 50 mm, better still greater than 70 mm,for example between 100 and 200 mm.

The rotor may comprise a rotor mass extending along the axis of rotationand arranged around a shaft. The shaft may comprise torque transmissionmeans for driving the rotor mass in rotation.

The rotor may or may not be cantilevered.

The machine can be inserted alone in a housing or inserted in a gearboxhousing. In this case, it is inserted in a housing which also houses agearbox.

Manufacturing Method

Another aspect, independently or in combination with the above, is amethod for manufacturing a stator for a rotating electrical machine, inparticular a stator as defined above, in which electrical conductors areplaced in the notches of a stator mass of the stator by inserting theminto the corresponding notches via one or both axial ends of the stator.

The same U-shaped electrical conductor can be placed in two differentnon-consecutive notches of the stator mass of the stator. In the casewhere an electrical conductor is U-shaped, it can be soldered to twoother electrical conductors on the same side of the machine.

Two I-shaped electrical conductors can be connected together beforehandin two different non-consecutive notches of the stator mass of thestator. In the case where an electrical conductor is I-shaped, it can besoldered to two other electrical conductors on two opposite sides of themachine.

In the stator, it is possible to electrically connect all the electricalconductors together which have a free end located at the samecircumferential position about the axis of rotation of the machine,regardless of their radial position.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosed stator may be better understood on reading the detaileddescription which follows, of non-limiting embodiments thereof, and onexamining the appended drawing, in which:

FIG. 1 is a schematic and partial perspective view of a stator.

FIG. 2 is a schematic and partial perspective view of the stator of FIG.1.

FIG. 3 is a detail perspective view of the stator of FIG. 1.

FIG. 4 is a schematic and partial cross-sectional view of the stator.

FIG. 5 is a schematic and partial cross-sectional view of the statormass of the stator.

FIG. 6 illustrates the variation of the radial air gap field, in Tesla,as a function of the angular position in degrees)(°.

FIG. 7 is a perspective view of an alternative embodiment.

FIG. 8 is a detail perspective view of the stator of FIG. 5.

FIG. 9 is a schematic and partial cross-sectional view of the stator ofFIG. 7.

FIG. 10 is a schematic and partial cross-sectional view of analternative embodiment.

DETAILED DESCRIPTION

FIGS. 1 to 5 show a stator 2 of a rotating electrical machine 1 alsocomprising a rotor, not shown. The stator makes it possible to generatea rotating magnetic field for driving the rotating rotor, in the contextof a synchronous motor, and in the case of an alternator, the rotationof the rotor induces an electromotive force in the electrical conductorsof the stator.

The examples illustrated below are schematic and the relative dimensionsof the various component elements have not necessarily been observed.

The stator 2 comprises electrical conductors 22, which are arranged innotches 21 formed between teeth 23 of a stator mass 25. The notches 21are closed.

The notches 21 are closed on the side of the air gap by material bridges27, each connecting two consecutive teeth of the stator mass 25, and onthe opposite side by a yoke 29. The yoke 29 and the teeth 23 are in onepiece. Where applicable, the yoke 29 can be traversed by longitudinalribs 31 of semi-circular section intended to house ducts for circulatinga coolant.

The electrical conductors 22 are for the most part in the form of pins,namely U or I pins, and which extend axially in the notches. A firstelectrical conductor housed in a first notch is electrically connectedto a second electrical conductor housed in a second notch, at the outletfrom said notches.

The first and second notches are non-consecutive. In the illustratedexample, they are separated by 7 other notches. Alternatively, the firstand second notches are separated by 3, 4, 5, 6, 8, 9, 10 or 11 othernotches, for example.

In particular, FIG. 2 shows the end surfaces 22 a of the first andsecond electrical conductors intended to receive the electricalconnection. The electrical connection is made in a plane perpendicularto the axis of rotation of the machine. The plane of the electricalconnection can be less than 40 mm away from the stator mass, inparticular approximately 27 mm away.

The electrical connection is formed on the electrical conductors justafter they exit the two notches, at one axial end of the stator mass.The two conductors each comprise an oblique portion 22 b, which convergetoward one another.

The electrical conductors are arranged in the notches in a distributedmanner, and they form a distributed winding, which is fractional in thedescribed example. In this example, the number of notches is 60. Thenumber of stator poles is 8. Thus, the ratio of the number ofnotches/the number of stator poles is 60/8.

The electrical conductors form a fractional winding, for which the ratioq, defined by q=Ne/(2 pm), is written as an irreducible fraction z/n, zand n being two non-zero integers, n being different from 1, where Ne isthe number of notches of the stator, m the number of phases of thewinding and p the number of pairs of stator poles. In particular, FIG. 4shows a one-phase coil in isolation in the case of a three-phasefractional winding. We then have q=60/(3×8)=5/2 for this machine with 60notches and 8 poles. A coil is formed by the outgoing electricalconductors of the same phase passing through adjacent notches, and bythe return electrical conductors of the same phase passing throughadjacent notches.

The electrical conductors 22 are arranged in a row in the notches 21, ina row of aligned electrical conductors.

The electrical conductors may have a generally rectangularcross-section, in particular with rounded corners. In the describedexample, they are superimposed radially in a single row. Thecircumferential dimension of an electrical conductor correspondssubstantially to the width of a notch. Thus, the notch comprises onlyone electrical conductor in its width. It can comprise severalelectrical conductors in its radial dimension. It comprises two in thedescribed example.

The electrical conductors 22 are made of copper or aluminum, or anyother conductive material enameled or coated with any other suitableinsulating coating.

FIG. 6 illustrates the variation of the radial air gap field due to thearmature reaction alone, in Tesla, as a function of the angular positionin degrees)(°. Curve A illustrates this variation for a stator withclosed notches, and is presented in comparison with curve B, whichillustrates this variation for a stator with semi-open notches, with anopening of 2 mm. It can be seen that the radial air gap field obtainedwith a stator with closed notches (curve A) is less rich in harmonics.

In the example which has just been described, a notch comprises twoelectrical conductors of different phases, and each electrical conductoris formed from a single strand.

In the alternative embodiment of FIGS. 7 to 9, each electrical conductorcomprises several pins, each forming a strand 32 within a notch. Thus,each electrical conductor comprises three strands 32. All the strands 32of the same electrical conductor 22 are electrically connected to eachother at the outlet of the notch, and to each of their two axial ends 22a.

Furthermore, the stator of FIGS. 5 and 6 comprises 63 notches and 6poles of the stator. Thus, the ratio of the number of notches/the numberof stator poles is 63/6.

Thus, the electrical conductors form a fractional winding, for which theratio q defined by q=Ne/(2 pm) is written as an irreducible fractionz/n, z and n being two non-zero integers, n being different from 1,where Ne is the number of notches of the stator, m the number of phasesof the winding and p the number of pairs of stator poles. In particular,FIG. 9 shows a one-phase coil in isolation in the case of a three-phasefractional winding. We then have q=63/(3×6)=7/2 for this machine with 63notches and 6 poles. A coil is formed by the outgoing electricalconductors of the same phase passing through adjacent notches, and bythe return electrical conductors of the same phase passing throughadjacent notches.

Each electrical conductor 22 is surrounded by an insulating sheet notvisible in the figures, making it possible to insulate the electricalconductors of the walls 33 and 36 of the notch and the electricalconductors 22 of different phases from one another within a notch.

In the described examples and as visible in FIG. 5, the notches 21 haveradial edges 33 which are parallel to one another, and in cross-sectionare in a plane perpendicular to the axis of rotation of the machine ofsubstantially rectangular shape.

The bottom 35 of the notches 21 is of a shape substantiallycomplementary to that of the electrical conductors 22, with theexception of a groove 40, as can be seen in FIG. 5.

The bottom 35 of the notches 21 is connected to the radial edges 33 byrounded edges or corners 38. The groove 40 of each notch 21 is centeredon the bottom of the notch 35 and extends along the axis of rotation ofthe machine. In an alternative embodiment, not shown, the groove is notcentered, or the bottom 35 comprises several grooves.

The grooves 40 have, in cross-section in a plane perpendicular to theaxis of rotation, a rounded shape, in particular substantiallysemi-circular. They present a depth p between 0.3 mm and 0.6 mm, forexample equal to 0.5 mm.

The presence of the grooves 40 leads to a localized constriction of thematerial bridges 27. Such a constriction allows a magnetic saturation ofthe sheet for a lower magnetic flux along the bridge 27, which limitsthe passage of the magnetic flux.

The smallest width I of the material bridges 27 is preferably between0.2 mm and 0.5 mm, for example equal to 0.35 mm.

The notches are generally rectangular in cross-section. All or part ofthe notches may comprise radial edges 33 having a rib 42, as illustratedin FIG. 10. Each rib 42 may extend parallel to the axis of rotation ofthe machine. This rib 42 is placed in a central part of the radial edges33, substantially halfway between the bottom of the notch 36 on the sideof the yoke 29 and the material bridge 27 closing it.

The stator mass 25 is formed from a bundle of magnetic sheets stackedalong the axis of rotation, the sheets for example being identical andexactly superimposed. They can be held together by clipping, gluing,rivets, tie rods, welds and/or any other technique. The magnetic sheetsare preferably made of magnetic steel. The teeth 23 of the stator mass25 may have complementary surface reliefs making it possible to clip thevarious sheets making up the stator mass 25 together.

The stator can be obtained by means of a manufacturing method in whichthe electrical conductors 22 are inserted into the notches 21 by one orboth axial ends of the stator, by sliding in the notches 21 along anaxis of rotation parallel to the longitudinal axis

In the stator, all the electrical conductors which have a free endlocated at the same circumferential position about the axis of rotationof the machine are electrically connected together, regardless of theirradial position.

Of course, the claimed invention is not limited to the embodiments whichhave just been described, and the rotor associated with the describedstator can be wound, with a squirrel cage or with permanent magnets, orelse with variable reluctance.

The expression “comprising a” should be understood as being synonymouswith “comprising at least one.”

1. A stator for a rotating electrical machine comprising a stator masscomprising teeth and notches between the teeth (23), each of the notchesbeing completely closed on an air gap side of the stator, electricalconductors housed in the notches, the electrical conductors forming afractional winding, for which a ratio q defined by q=Ne/(2 pm) iswritten as an irreducible fraction z/n, z and n being two non-zerointegers, n being different from 1, where Ne is the number of statornotches, m is the number of winding phases and p is the number of pairsof stator poles, wherein at least some of the electrical conductors arein the form of pins.
 2. The stator according to claim 1, wherein theelectrical conductors form a distributed winding.
 3. The statoraccording to claim 1, wherein a majority of the electrical conductorsare in the form of pins extending axially into the notches.
 4. Thestator according to claim 1, wherein the notches are closed on the airgap side by a magnetic hoop.
 5. The stator according to claim 4, whereinthe magnetic hoop has at least one localized constriction formed definedby at least one groove.
 6. The stator according to claim 1, wherein atleast one of said notches is continuously closed on the air gap side bya material bridge formed in one piece with the teeth defining the notch.7. The stator according to claim 1, wherein the material bridges eachhaving at least one localized constriction defined by at least onegroove.
 8. The stator according to claim 1, wherein the notches areclosed on the side opposite the air gap side by a yoke attached to orintegral with the teeth.
 9. The stator according to claim 1, wherein theelectrical conductors have a generally rectangular cross-section. 10.The stator according to claim 1, wherein each notch comprises two toeight electrical conductors, each electrical conductor comprising one ormore strands.
 11. The stator according to claim 1, wherein at least oneof said electrical conductors is in the shape of a U-pin comprising afirst and a second leg extending axially respectively in first A andsecond R of said notches, the first A and second R of said notches beingseparated by a number Nd of teeth, the number Nd of teeth being strictlygreater than
 5. 12. The stator according to claim 1, wherein at leastone of said notches comprises radial edges having a rib.
 13. The statoraccording to claim 1, wherein at least one of said notches has arectilinear or arcuate shaped bottom.
 14. The stator according to claim1, wherein the notches are configured to allow the passage of a coolant.15. A stator for a rotating electrical machine comprising a stator masscomprising teeth and notches between the teeth, each of the notchesbeing at least partially closed on an air gap side of the stator,electrical conductors housed in the notches and being distributed in atleast two layers the electrical conductors forming a fractional winding,for which a ratio q defined by q=Ne/(2 pm) is written as an irreduciblefraction z/n, z and n being two non-zero integers, n being differentfrom 1, where Ne is the number of stator notches, m is the number ofwinding phases and p is the number of pairs of stator poles, wherein atleast some of the electrical conductors are in the form of pins.
 16. Arotating electrical machine comprising a stator according to claim 1 anda rotor.
 17. The stator of claim 1 wherein the pins are U- or I-shapedpins.
 18. The stator of claim 9 wherein the electrical conductors haverounded corners
 19. The stator of claim 15 wherein the electricalconductors are distributed in only two layers.